1. S.Ducasse
Stéphane Ducasse
Stephane.Ducasse@univ-savoie.fr
http://www.listic.univ-savoie.fr/~ducasse/
1
A Taste of Smalltalk

2. S.Ducasse
License: CC-Attribution-ShareAlike 2.0
http://creativecommons.org/licenses/by-sa/2.0/
2

3. S.Ducasse 3
Goals
• Two examples:
• ‘hello world’
• A tamagotchi
• To give you an idea of:
• the syntax
• the elementary objects and classes
• the environment

4. S.Ducasse 4
An Advice
You do not have to know everything!!!
•“Try not to care - Beginning Smalltalk programmers
often have trouble because they think they need to
understand all the details of how a thing works
before they can use it. This means it takes quite a
while before they can master Transcript show: ‘Hello
World’. One of the great leaps in OO is to be able to
answer the question "How does this work?" with "I
don’t care"“. Alan Knight. Smalltalk Guru
• We will show you how to learn and find your way

5. S.Ducasse 5
Some Conventions
• Return Values
1 + 3 -> 4
Node new -> aNode
• Method selector #add:
• Method scope conventions
• Instance Method defined in class Node:
Node>>accept: aPacket
• Class Method defined in class Node (in the class of
the the class Node)
Node class>>withName: aSymbol
• aSomething is an instance of the class Something

6. S.Ducasse 6
Roadmap
• “hello world”
• Syntax
• a tamagotchi

7. S.Ducasse 7
Hello World
• Transcript show: ‘hello world’
• At anytime we can dynamically ask the system to
evaluate an expression. To evaluate an expression,
select it and with the middle mouse button apply
doIt.
• Transcript is a special object that is a kind of
standard output.
• It refers to a TextCollector instance associated with
the launcher.
• In Squeak Transcript is dead slow...

8. S.Ducasse 8
Transcript show: ‘hello world’

9. S.Ducasse 9
Everything is an Object
– The workspace is an object.
– The window is an object: it is an instance of SystemWindow.
– The text editor is an object: it is an instance of ParagraphEditor.
– The scrollbars are objects too.
– ‘hello word’ is an object: it is aString instance of String.
– #show: is a Symbol that is also an object.
– The mouse is an object.
– The parser is an object: instance of Parser.
– The compiler is also an object: instance of Compiler.
– The process scheduler is also an object.
– The garbage collector is an object: instance of ObjectMemory.
– Smalltalk is a consistent, uniform world written in itself. You can learn
how it is implemented, you can extend it or even modify it. All the code
is available and readable

10. S.Ducasse 10
Smalltalk Object Model
• ***Everything*** is an object
Only message passing
Only late binding
• Instance variables are private to the object
• Methods are public
• Everything is a pointer
• Garbage collector
• Single inheritance between classes
• Only message passing between objects

11. S.Ducasse 11
Roadmap
• Hello World
• First look at the syntax
• a Tamagotchi

12. S.Ducasse 12
Power & Simplicity: The Syntax on a
PostCard
•exampleWithNumber: x
•“A method that illustrates every part of Smalltalk method syntax except
primitives. It has unary, binary, and key word messages, declares arguments
and temporaries (but not block temporaries), accesses a global variable (but
not and instance variable), uses literals (array, character, symbol, string,
integer, float), uses the pseudo variable true false, nil, self, and super, and has
sequence, assignment, return and cascade. It has both zero argument and one
argument blocks. It doesn’t do anything useful, though”
• |y|
• true & false not & (nil isNil) ifFalse: [self halt].
• y := self size + super size.
• #($a #a ‘a’ 1 1.0)
• do: [:each | Transcript
•show: (each class name);
•show: (each printString);
• show: ‘ ‘].
• ^ x < y

13. S.Ducasse 13
Yes ifTrue: is sent to a boolean
Weather isRaining
ifTrue: [self takeMyUmbrella]
ifFalse: [self takeMySunglasses]
ifTrue:ifFalse is sent to an object: a boolean!

14. S.Ducasse 14
Yes a collection is iterating on itself
•#(1 2 -4 -86)
• do: [:each | Transcript show: each abs
printString ;cr ]
•> 1
•> 2
•> 4
•> 86
•Yes we ask the collection object to perform the
loop on itself

15. S.Ducasse 15
DoIt, PrintIt, InspectIt and
Accept
• Accept = Compile: Accept a method or a class
definition
• DoIt = send a message to an object
• PrintIt = send a message to an object + print
the result (#printOn:)
• InspectIt = send a message to an object +
inspect the result (#inspect)

16. S.Ducasse 16
Objects send messages
• Transcript show: ‘hello world’
• The above expression is a message
• the object Transcript is the receiver of the message
• the selector of the message is #show:
• one argument: a string ‘hello world’
• Transcript is a global variable (starts with an
uppercase letter) that refers to the Launcher’s
report part.

17. S.Ducasse 17
Vocabulary Point
Message passing or sending a message is
equivalent to
invoking a method in Java or C++
calling a procedure in procedural languages
applying a function in functional languages
of course the last two points must be considered
under the light of polymorphism

18. S.Ducasse 18
Roadmap
• Hello World
• First look at the syntax
• A tamagotchi

19. S.Ducasse 19
Tamagotchi
• Small entity
– Its own night and day cycle
– Eating, sleeping, been hungry, been satisfied
– Changing color to indicate its mood

20. S.Ducasse 20
Tomagotchi
woken up
sleeping
satisfied
hungry
fallAsleep
wakeUp
night
isSatisfied
eat
day
isHungry

21. S.Ducasse 21
Instantiating…
• To create a tomagoshi:
• Tomagoshi newStandAlone openInWorld

22. S.Ducasse 22
How to Define a Class (Sq)
• Fill the template:
NameOfSuperclass subclass: #NameOfClass
instanceVariableNames: 'instVarName1'
classVariableNames: 'ClassVarName1
ClassVarName2'
poolDictionaries: ''
category: ’category name'

23. S.Ducasse 23
Tomagoshi (Sq)
• For example to create the class Tomagoshi
Morph subclass: #Tomagoshi
instanceVariableNames: ‘tummy hunger
dayCount isNight'
classVariableNames: ''
poolDictionaries: ''
category: ’TOMA'

24. S.Ducasse 24
Class Comment!
• I represent a tomagoshi. A small virtual animal that
have its own life.
• dayCount <Number> represents the number of hour
(or tick) in my day and night.
• isNight <Boolean> represents the fact that this is
the night.
• tummy <Number> represents the number of times
you feed me by clicking on me.
• hunger <Number> represents my appetite power.
• I will be hungry if you do not feed me enough, but
I'm selfish so as soon as I' satisfied I fall asleep
because I do not have a lot to say.

25. S.Ducasse 25
How to define a method?
message selector and argument names
"comment stating purpose of message"
| temporary variable names |
statements
Tomagoshi>>initializeToStandAlone
“Initialize the internal state of a newly created tomagoshi”
super initializeToStandAlone.
tummy := 0.
hunger := 2 atRandom + 1.
self dayStart.
self wakeUp

26. S.Ducasse 26
Initializing
Tomagoshi>>initializeToStandAlone
“Initialize the internal state of a newly created
tomagoshi”
super initializeToStandAlone.
tummy := 0.
hunger := 2 atRandom + 1.
self dayStart.
self wakeUp

27. S.Ducasse 27
dayStart
Tomagoshi>>dayStart
night := false.
dayCount := 10

28. S.Ducasse 28
Step
step
“This method is called by the system at regurlar time interval. It
defines the tomagoshi behavior.”
self timePass.
self isHungry
ifTrue: [self color: Color red].
self isSatisfied
ifTrue:
[self color: Color blue.
self fallAsleep].
self isNight
ifTrue:
[self color: Color black.
self fallAsleep]

29. S.Ducasse 29
Time Pass
Tomagoshi>>timePass
"Manage the night and day alternance"
Smalltalk beep.
dayCount := dayCount -1.
dayCount isZero
ifTrue:[ self nightOrDayEnd.
dayCount := 10].
self digest
Tomagoshi>>nightOrDayEnd
"alternate night and day"
night := night not

30. S.Ducasse 30
Digest
Tomagoshi>>digest
"Digest slowly: every two cycle, remove one from the
tummy”
(dayCount isDivisibleBy: 2)
ifTrue: [ tummy := tummy -1]

31. S.Ducasse 31
Testing
Tomagoshi>>isHungry
^ hunger > tummy
Tomagoshi>>isSatisfied
^self isHungry not
Tomagoshi>>isNight
^ night

32. S.Ducasse 32
State
Tomagoshi>>wakeUp
self color: Color green.
state := self wakeUpState
Tomagoshi>>wakeUpState
"Return how we codify the fact that I sleep"
^ #sleep
Tomagoshi>> isSleeping
^ state = self wakeUpState

33. S.Ducasse 33
Eating
Tomagoshi>>eat
tummy := tummy + 1

34. S.Ducasse 34
Time and Events
Tomagoshi>>stepTime
"The step method is executed every steppingTime
ms"
^ 500
Tomagoshi>>handlesMouseDown: evt
"true means that the morph can react when the mouse
down over it"
^ true
Tomagoshi>>mouseDown: evt
self eat

35. S.Ducasse 35
Summary
What is a message?
What is the message receiver?
What is the method selector?
How to create a class?
How to define a method?